This invention generally relates to a connector lock structure, and more particularly to a connector lock structure having a mechanism for releasing a locked condition of connector housings.
Hitherto, there has been a lock structure shown in FIGS. 5 and 6 (see, for example, JP-A-2000-150069), which serves as a structure for connecting male and female connector housings to each other, for locking this connected condition, and for releasing this locked condition.
The lock structure shown in FIGS. 5 and 6 is configured so that a lock portion 1 having a lock arm 3 and a releasing arm 5 is formed integrally with the female connector housing.
As shown in FIG. 6, the lock arm 3 includes two curved leg portions 3a formed in such a way as to upwardly protrude and extend from an outer wall 7, two arm portions 3b respectively and horizontally extending from the two leg portions 3a along a connector fitting direction toward a latch portion of a counterpart connector, and an engaging portion 3c which is formed in such a manner as to connect ends of the two arm portions 3b to each other and has a locking claw 3d. 
As shown in FIG. 6, the releasing arm 5 includes two leg portions 5a and two arm portions 5b. The two leg portions 5a upwardly protrudes and extends from the outer wall 7 and are thinner than the leg portions 3a. The two arm portions 5b is respectively formed on the two leg portions 5a. Each of the two leg portions 5a is formed at an outer side of an associated one of the leg portions 3a and at nearly the same position as that of the associated leg portion 3a. 
The arm portions 5b are formed so that end parts thereof extend in a direction opposite to the engaging portion 3c and are connected to each other to thereby form the releasing portion 5c, and that the other end parts thereof extend toward and are connected to the engaging portion 3c. 
In a case of releasing the locked condition of the lock portion 1, the releasing portion 5c is depressed in the direction of an arrow A as shown in FIG. 6. The releasing arm 5 turns in response to a force exerted on the releasing portion 5c so as to surely upwardly and pivotally move the engaging portion 3c in the direction of an arrow B around each of the leg portions 5a. As a result, the locking claw 3d is disengaged from the latch portion of the counterpart connecter (not shown) to release the locked condition.
Because the releasing arm 5 has the leg portions 5a, the engaging portion 3c surely displaces in a lock releasing direction B in response to a force applied to the releasing portion 5c regardless of a direction and an angle of application of the force. Consequently, cancellability of the structure is enhanced.
However, in the case of the lock structure of the related lock portion 1, when the engaging portion 3c is engaged with and disengaged from the latch portion of the counterpart connector, the lock arm 3 and the releasing arm 5 swing around the leg portions 3a and 5a protruding upwardly from the outer wall 7 of the connector housing, respectively.
Thus, bending stresses are apt to be concentrated at bent portions k1 at each of which an associated one of the leg portions 3a intersects with an associated one of the arm portions 3b, bent portions k2 at each of which an associated one of the leg portions 5a intersects with an associated one of the arm portions 5b, and corner portions k3 and k4 at which the leg portions 3a and 5a continued to the outer wall 7 of the connector housing, respectively. Fatigue due to stress concentration in the leg portions 3a and 5a may result in permanent deflections thereof and may cause reduction in an engaging strength of the engaging portion 3c, or fatigue destruction thereof.
In the lock structure of the related lock portion 1, a position, at which the engaging portion 3c of the lock arm 3 is equipped, is away from the outer wall 7 of the connector housing by a height h of each of the leg portions 3a. Thus, the lock structure of the related lock portion 1 has a problem in that the size of the connector housing increase owing to increase in the dimension of the outside diameter of the connector housing, which is caused by outward protrusion of the engaging portion 3c. 